In late years, “touch panels” have come to be widely used which are installed on surfaces of flat panel displays (FPD) included in a mobile phone, a portable device for electronic documents, a vending machine, a car navigation system, and the like.
The “touch panels” described above are largely divided into resistive ones and capacitive ones. The “resistive touch panel” has a main part which includes a transparent substrate formed of a resin film, an X-coordinate- (or Y-coordinate-) detecting electrode sheet and a Y-coordinate- (or X-coordinate-) detecting electrode sheet provided on the substrate, and an insulating spacer provided between these sheets. Here, although the X-coordinate-detecting electrode sheet and the Y-coordinate-detecting electrode sheet described above are spatially separated, both coordinate-detecting electrode sheets are configured to come into electrical contact with each other when pressed by a pen or the like, and to detect the position (X-coordinate and Y-coordinate) which the pen touched. The sheets are designed to trace the movement of the pen and recognize its coordinates, making it possible for the character to be inputted as a result. On the other hand, the “capacitive touch panel” has a structure where an X-coordinate- (or Y-coordinate-) detecting electrode sheet and a Y-coordinate- (or X-coordinate-) detecting electrode sheet are laminated with an insulating sheet in between, and an insulator such as glass is dispose on these. With this setup, when a finger approaches the above-described insulator such as glass, the sheets detect the position because electric capacitances of the X-coordinate-detecting electrode and the Y-coordinate-detecting electrode change.
Conventionally, transparent conductive films formed of ITO (indium oxide-tin oxide) and the like have been widely used as a conductive material for a circuit pattern of electrodes and the like (see Patent Document 1). Along with an increase in size of touch panels, mesh-structure metal thin lines (metal films) as disclosed in Patent Document 2, Patent Document 3, and the like are beginning to be used.
Comparison between the transparent conductive film and the metal thin line (metal film) described above shows the transparent conductive film has an advantage that, due to its excellent transmittance in a visible wavelength range, the circuit pattern of electrodes and the like is less visible, but the transparent conductive film has a disadvantage that it is unsuitable for the purpose of increasing the size and response speed of touch panels because its electrical resistance value is higher than that of the metal thin line (metal film). The metal thin line (metal film), on the other hand, is suitable for the purpose of increasing the size and response speed of touch panels because of its low electrical resistance value, but has a disadvantage that, due to a high reflectance in the visible wavelength range, the circuit pattern may be visible under highly bright illumination even if the metal thin line is formed into a fine mesh structure, which results in a decrease in product value.
In view of the above, in order to take advantage of the characteristic of the above-mentioned metal thin line (metal film) having a low electrical resistance value, a method is proposed that includes interposing a metal absorption layer (referred to as a blackened film) made of metal oxide between a transparent substrate formed of a resin film and a metal thin line (metal film) (see Patent Document 4 and Patent Document 5), and thereby reducing reflection on the metal thin line (metal film) observed on the transparent substrate side.
Moreover, from the standpoint of achieving efficient deposition of the metal oxide, the above-described metal absorption layer made of metal oxide is usually deposited continuously on a surface of a long resin film by, for example, reactive sputtering which uses a metal target (metal material) and a reactive gas, and a metal layer is continuously deposited on the metal absorption layer thus deposited by, for example, sputtering which uses a metal target (metal material) such as copper. In such a manner, a laminate film used in the fabrication of an electrode substrate film is manufactured.
Here, the electrode substrate film applied to a touch panel or the like is manufactured by: etching a layered film included in a laminate film using an etching liquid such as an aqueous solution of copper(II) chloride or an aqueous solution of ferric chloride, the laminate film including a transparent substrate formed of a resin film and the layered film formed of a metal absorption layer provided on the substrate and of a metal layer; and forming a circuit pattern of electrodes and the like from the layered film (metal absorption layer and metal layer) of the laminate film.
For this reason, the laminate film used in the fabrication of the electrode substrate film is required to have such characteristics that the layered film (metal absorption layer and metal layer) is easily etched by an etching liquid such as an aqueous solution of copper(II) chloride or an aqueous solution of ferric chloride, and that the circuit pattern of electrodes and the like formed by etching processing is less visible under highly bright illumination.